1. Field of the Invention
The present invention relates to a vacuum vessel, and in particular, to a vacuum vessel which has built-in spacers for spacing first and second substrates apart from each other by a predetermined distance, and an electron emission display device using the vacuum vessel.
2. Description of the Related Art
Generally, electron emission devices are classified into those using hot cathodes as an electron emission source and those using cold cathodes as the electron emission source. There are several types of cold cathode electron emission devices, including a field emitter array (FEA) type, a metal-insulator-metal (MIM) type, a metal-insulator-semiconductor (MIS) type, and a surface conduction emitter (SCE) type.
Although the electron emission devices are differentiated by specific structure depending upon the types thereof, they all basically have electron emission regions formed on a substrate, and driving electrodes for controlling the on/off and amount of electron emission from the electron emission regions. The electron emission devices can be used as an electron emission structure for a light source, such as a backlight or an image display device.
With the typical structure of the electron emission display device using the electron emission device, electron emission regions and driving electrodes are formed on a first substrate, and phosphor layers are formed on a surface of a second substrate facing the first substrate together with an anode electrode that keeps the phosphor layers at a high potential state. The first and the second substrates are sealed together at their peripheries using a sealing member, and the interior thereof is exhausted to form a vacuum vessel so that the electrons can be fluently emitted and migrated therein. A strong compression force is applied to the vacuum vessel due to the pressure difference between the interior and exterior thereof. A plurality of spacers are provided within the vacuum vessel to prevent vacuum vessel from breaking due to the compressive force. The spacers are attached to any one of the first the second substrates using an adhesive layer, and placed within the active area along with the electron emission regions and the phosphor layers.
With such a vacuum vessel, when spacers are fitted to one of the first and the second substrates and the interior thereof is evacuated, the spacers and the other of the first and the second substrates spaced apart from each other without an intervening adhesive layer are held tightly in contact with each other so that an impact is applied to the spacers, and the spacers are liable to be broken due to this impact.
The electron emission display device further has a non-active area located between the active area and the sealing member that does not serve to display an image. With the distribution of the stresses applied to the first and the second substrates after the exhausting, the stress applied to the non-active area is greater than the stress applied to the active area. This is because the structure for absorbing and withstanding the pressure of the two substrates is not present in the non-active area. Accordingly, cracks are likely to occur in the vacuum vessel due to the relatively large stress in the non-active area.
As spacers are attached to the substrate using an adhesive layer, the adhesion thereof with respect to the substrate is relatively weak. Consequently, some spacers are inclined or detached from the substrate during the exhausting process so that the pressure applied to the vacuum vessel is not uniformly distributed. As a result, the inclined spacers can block the paths of the electron beams, thus deteriorating the display characteristic. Moreover, as the wall type spacers have a high sectional aspect ratio and a long length, they are prone to twisting. For this reason, in a vacuum vessel using the wall type spacers, the spacers are likely to be twisted or inclined after the exhausting. Therefore, what is needed is an improved design for a vacuum vessel and an electron emission display device having the same that is better able to withstand and absorb the pressure caused by the vacuum vessel while overcoming the above problems.